1. Field of the Invention
The invention relates to a printing unit cylinder for a rotary printing machine and, more particularly, to a gap strip positioned in the cylinder gap of the printing unit cylinder. The gap strip is supported on the bottom of said cylinder gap and is removably fastened in the cylinder gap. The gap strip extends from the gap a distance to permit gap strips of two cooperating cylinders to contact each other.
2. Background Information
In printing plate cylinders and blanket cylinders of an offset rotary printing press, it is known to insert an element in the cylinder groove or gap for absorbing shocks and vibrations imparted to the cylinder. U.S. Pat. No. 4,742,769 discloses a filler element inserted in a cylinder gap or groove that extends axially on the cylinder. The filler element is strip-like in shape and is supported on the bottom of the cylinder gap. The filler element is of lesser axial length than the cylinder. The filler element is operable to absorb shocks which occur in the area of the cylinder gaps by cooperating with a filler element in an adjacently positioned cylinder. As further disclosed in U.S. Pat. No. 4,742,769 and also in U.S. Pat. No. 4,815,380, the filler element extends over flattened regions of the cylinder at the gap opening. This arrangement results in a rigid mounting of the filler element in the gap.
It is known that the contact between the elastic blanket on the blanket cylinder and the rigid filler element generates considerable shocks when two adjacently positioned cylinders roll across each other, resulting in vibrations of the cylinders. Adapting the outer contour of the filler element to the theoretical diameter of the cylinder cannot prevent the vibrations from occurring, especially in view of the interaction of blankets with different degrees of hardness and the cooperation between a blanket and printing plate in another cylinder combination. These attempts to eliminate the effects of vibrations, which are detrimental to the printed image, have not proved to be satisfactory.
U.S. Pat. No. 4,790,245 discloses a support assembly for a cylinder groove in a plate or blanket cylinder of a rotary printing machine. The support assembly includes a support bar attached to a holding rail at the bottom of the groove in a manner to permit adjustments in the height of the support bar with respect to the theoretical diameter of the cylinder. The support bar is connected to the holding rail by a tensioning device which consists of individual parts featuring inclined areas that facilitate adjustments to the height of the support bar in the groove. Disadvantages result with this adjustment assembly in the operation of the printing machine producing cylinder wash-up, penetration of dust and solvents into the adjustment assembly and solidification shortly afterwards. Thus, this known solution does not permit sensitive adjustment of the support bar in sustained operation of the printing press. Moreover, the change of blankets or printing plates requires complicated procedures when removing the parts of the support bar from the cylinder gap and putting them in place again after having changed blankets and printing plates.
U.S. Pat. No. 2,714,852 discloses another example of a bar member positioned in the axial groove of a printing press transfer cylinder. The bar member is used to tension the ends of the transfer blanket and snugly draw the blanket around the periphery of the cylinder.
While it is known to provide a gap strip of a transfer cylinder or the like in a rotary printing press to reduce shocks and vibrations, the known strips require complicated mounting means and do not satisfactorily reduce vibrations. Therefore, there is need to provide a simple construction which is easy to insert in the cylinder gap, and which guarantees reliable vibration absorption in the area of the cylinder gap.